.\" @(#)$Id: PAPI_profil.3,v 1.11 2004/10/02 18:52:49 terpstra Exp $
.TH PAPI_profil 3 "September, 2004" "PAPI Programmer's Reference" "PAPI"

.SH NAME
PAPI_profil \- generate a histogram of hardware counter overflows vs. PC addresses

.SH SYNOPSIS
.B C Interface
.nf
.B #include <papi.h>
.BI "int PAPI_profil(void * " buf, " unsigned " bufsiz, " unsigned long " offset, 
.BI "                unsigned " scale, " int " EventSet, " int " EventCode, "  int "  threshold,
.BI "                int " flags );
.fi
.LP
.B Fortran Interface
.nf
.I The profiling routines have no Fortran interface.
.fi

.SH DESCRIPTION
.B PAPI_profil() 
provides hardware event statistics by profiling the occurence of specified hardware
counter events. It is designed to mimic the UNIX SVR4 profil call. The statistics are 
generated by creating a histogram of hardware counter 
event overflows vs. program counter addresses for the current process. The histogram is 
defined for a specific region of program code to be profiled, and the identified region 
is logically broken up into a set of equal size subdivisions, each of which corresponds 
to a count in the histogram. With each hardware event overflow, the current subdivision 
is identified and its corresponding histogram count is incremented. These counts establish 
a relative measure of how many hardware counter events are occuring in each code subdivision. 
The resulting histogram counts for a profiled region can be used to identify those program  
addresses that generate a disproportionately high percentage of the event of interest.
.LP
Events to be profiled are specified with the
.I EventSet
and
.I EventCode
parameters. More than one event can be simultaneously profiled by calling
.B PAPI_profil()
several times with different
.I EventCode
values. Profiling can be turned off for a given event by calling
.B PAPI_profil()
with a
.I threshold
value of 0.

.SH ARGUMENTS
.I *buf
-- pointer to a buffer of 
.I bufsiz 
bytes in which the histogram counts are stored in an array of unsigned short, unsigned int, or
unsigned long long values, or 'buckets'. The size of the buckets is determined by values in the
.I flags
argument.
.LP
.I bufsiz
-- the size of the histogram buffer in bytes. It is computed from the length of the code region to be 
profiled, the size of the buckets, and the scale factor as discussed below.
.LP
.I offset
-- the start address of	the region to be profiled.
.LP
.I scale
-- broadly and historically speaking, a contraction factor that indicates how much
smaller the histogram buffer is than the region to be profiled. More
precisely, scale is interpreted as an unsigned 16-bit fixed-point
fraction with the decimal point implied on the left. Its value is the
reciprocal of the number of addresses in a subdivision, per counter of
histogram buffer. Below is a table of representative values for scale:
.LP
.TS
allbox tab($);
cI  s  s
lw lw  lw.
T{
Representative values for the scale variable
T}
HEX$DECIMAL$DEFININTION
0x20000$131072$Maps precisely one instruction address to a unique bucket in buf.
0x10000$ 65536$Maps precisely two instruction addresses to a unique bucket in buf.
 0xFFFF$ 65535$Maps approximately two instruction addresses to a unique bucket in buf.
 0x8000$ 32768$Maps every four instruction addresses to a bucket in buf.
 0x4000$ 16384$Maps every eight instruction addresses to a bucket in buf.
 0x0002$     2$Maps all instruction addresses to the same bucket in buf.
 0x0001$     1$Undefined.
 0x0000$     0$Undefined. 
.TE
.LP
.LP
Historically, the scale factor was introduced to allow the allocation of buffers smaller than
the code size to be profiled. Data and instruction sizes were assumed to be multiples of 16-bits.
These assumptions are no longer necessarily true. 
.B PAPI_profil
has preserved the traditional definition of scale where appropriate, 
but deprecated the definitions for 0 and 1 (disable scaling) and extended
the range of scale to include 65536 and 131072 to allow for exactly two 
addresses and exactly one address per profiling bucket.
.LP
The value of bufsiz is computed as follows: 
.LP
.I bufsiz = (end - start)*(bucket_size/2)*(scale/65536)
where
.LP
.I bufsiz
- the size of the buffer in bytes
.LP
.I end, start
- the ending and starting addresses of the profiled region
.LP
.I bucket_size
- the size of each bucket in bytes; 2, 4, or 8 as defined in
.I flags
.LP
.I scale
- as defined above
.LP
.I EventSet 
-- The PAPI EventSet to profile. This EventSet is marked as profiling-ready, but profiling
doesn't actually start until a 
.B PAPI_start()
call is issued.
.LP
.I EventCode
-- Code of the Event in the EventSet to profile. This event must already be a member of the EventSet.
.LP
.I threshold 
-- minimum number of events that must occur before the PC is sampled. If hardware overflow
is supported for your substrate, this threshold will trigger an interrupt when reached. 
Otherwise, the counters will be sampled periodically and the PC will be recorded for the
first sample that exceeds the threshold. If the value of threshold is 0, profiling will be
disabled for this event.

.LP
.I flags 
-- bit pattern to control profiling behavior. Defined values are shown in the table below:
.LP
.TS
allbox tab($);
cI  s
lB lw.
T{
Defined bits for the flags variable
T}
PAPI_PROFIL_POSIX$T{
Default type of profiling, similar to 
.BR profil (3).
T}
PAPI_PROFIL_RANDOM$T{
Drop a random 25% of the samples.
T}
PAPI_PROFIL_WEIGHTED$T{
Weight the samples by their value.
T}
PAPI_PROFIL_COMPRESS$T{
Ignore samples as values in the hash buckets get big.
T}
PAPI_PROFIL_BUCKET_16$T{
Use unsigned short (16 bit) buckets, This is the default bucket.
T}
PAPI_PROFIL_BUCKET_32$T{
Use unsigned int (32 bit) buckets.
T}
PAPI_PROFIL_BUCKET_64$T{
Use unsigned long long (64 bit) buckets.
T}
PAPI_PROFIL_FORCE_SW$T{
Force software overflow in profiling.
T}

.TE

.SH RETURN VALUES
On success, this function returns
.B "PAPI_OK."
 On error, a non-zero error code is returned.

.SH ERRORS
.TP
.B "PAPI_EINVAL"
One or more of the arguments is invalid.
.TP
.B "PAPI_ENOMEM"
Insufficient memory to complete the operation.
.TP
.B "PAPI_ENOEVST"
The EventSet specified does not exist.
.TP
.B "PAPI_EISRUN"
The EventSet is currently counting events.
.TP
.B "PAPI_ECNFLCT"
The underlying counter hardware can not count this event and other events
in the EventSet simultaneously.
.TP
.B "PAPI_ENOEVNT"
The PAPI preset is not available on the underlying hardware. 

.SH EXAMPLES
.nf
.if t .ft CW
int retval;
unsigned long length;
PAPI_exe_info_t *prginfo;
unsigned short *profbuf;

if ((prginfo = PAPI_get_executable_info()) == NULL)
  handle_error(1);

length = (unsigned long)(prginfo->text_end - prginfo->text_start);

profbuf = (unsigned short *)malloc(length);
if (profbuf == NULL)
  handle_error(1);
memset(profbuf,0x00,length);
 .
 .
 .
if ((retval = PAPI_profil(profbuf, length, start, 65536, EventSet, 
                PAPI_FP_INS, 1000000, PAPI_PROFIL_POSIX | PAPI_PROFIL_BUCKET_16)) != PAPI_OK)
  handle_error(retval);
.if t .ft P
.fi

.SH BUGS
If you call PAPI_profil, PAPI allocates buffer space that will not be
freed if you call PAPI_shutdown or PAPI_cleanup_eventset.  To clean all 
memory, you must call PAPI_profil on the Events with a 0 threshold.

.SH SEE ALSO
.BR PAPI_sprofil "(3), "
.BR PAPI_overflow "(3), "
.BR PAPI_get_executable_info "(3) "

